學習學習mysql内置數學函數，先進入mysql：
C:\Users\Administrator>cd /d D:\MySQL Server 5.5\bin
D:\MySQL Server 5.5\bin>mysql -u root -p
Enter password: ********
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.5.28 MySQL Community Server (GPL)
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Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> 如直接輸入以下指令，卻出現：
說明沒有設定系統的環境變量。
我們需要把Mysql bin檔案夾的位址添加到windows的“環境變量”/“系統變量”/path 中
如出現
ERROR 2003 (HY000): Can't connect to MySQL server on 'localhost' (10061)的錯誤，應該是mysql服務沒有開啟。以管理者身份運作cmd，開啟即可。還不懂就看：
數學函數：
abs(x) 傳回數字的絕對值
floor(x) 傳回不大于x的最大整數
rand() 傳回0至1的随機數
rand(x) 也傳回随機數，不過x作為種子
值
mysql> select abs(-2),floor(1.5),rand(),rand(),PI();
+---------+------------+--------------------+--------------------+----------+
| abs(-2) | floor(1.5) | rand() | rand() | PI() |
+---------+------------+--------------------+--------------------+----------+
| 2 | 1 | 0.8543179415672253 | 0.6597909654116174 | 3.141593 |
+---------+------------+--------------------+--------------------+----------+ TRUNCAT用于單純的截取小數。
mysql> select TRUNCATE(5.242354,4);
+----------------------+
| TRUNCATE(5.242354,4) |
+----------------------+
| 5.2423 |
+----------------------+ round()四舍五入取最近整數。
round(x,y)保留x小數點後y位的值
mysql> select round(5.242354,4);
+-------------------+
| round(5.242354,4) |
+-------------------+
| 5.2424 |
+-------------------+
mysql> select round(1.4),round(1.5),round(1.6);
+------------+------------+------------+
| round(1.4) | round(1.5) | round(1.6) |
+------------+------------+------------+
| 1 | 2 | 2 |
+------------+------------+------------+ sign(x) 判斷x的正負性。
x>0: 1
x<0: -1
x=0: 0
mysql> select sign(4),sign(-4),sign(0);
+---------+----------+---------+
| sign(4) | sign(-4) | sign(0) |
+---------+----------+---------+
| 1 | -1 | 0 |
+---------+----------+---------+ pow(x,y)
sqrt(x)
EXP(x) 傳回e的x乘方後的值
mod(x,y) 傳回 x mod y的值
log(x) 傳回
的值
log10(x)
mysql> select pow(2,6),sqrt(64),exp(2),mod(65,64),log(64),log10(100);
+----------+----------+------------------+------------+--------------------+------------+
| pow(2,6) | sqrt(64) | exp(2) | mod(65,64) | log(64) | log10(100) |
+----------+----------+------------------+------------+--------------------+------------+
| 64 | 8 | 7.38905609893065 | 1 | 4.1588830833596715 | 2 |
+----------+----------+------------------+------------+--------------------+------------+ 和角度相關的函數：
radians(x) 角度轉弧度
degrees(x) 弧度轉角度
mysql> select radians(180),degrees(PI());
+-------------------+---------------+
| radians(180) | degrees(PI()) |
+-------------------+---------------+
| 3.141592653589793 | 180 |
+-------------------+---------------+ 三角函數相關的函數：
mysql> select sin(PI()/2),cos(PI()/2.0),acos(0),tan(PI()/4.0),atan(1);
+-------------+-----------------------+--------------------+--------------------+--------------------+
| sin(PI()/2) | cos(PI()/2.0) | acos(0) | tan(PI()/4.0) | atan(1) |
+-------------+-----------------------+--------------------+--------------------+--------------------+
| 1 | 6.123233995736766e-17 | 1.5707963267948966 | 0.9999999999999999 | 0.7853981633974483 |
+-------------+-----------------------+--------------------+--------------------+--------------------+ 參數都是弧度。